In the field of medicine, injector heads have been used in angiographic examinations to deliver contrast agents into blood vessels of patients. The injector head is disposed with a plunger which is controlled to be slidable in an anteroposterior direction. The injector head is mounted with a syringe having a substantially cylindrical shape. Moreover, a piston to be connected to the plunger is disposed inside the syringe.
In a state where the syringe is mounted on the injector head, the plunger and the piston are connected, and as the plunger is moved forward, the piston is forced by the plunger to move forward to deliver a liquid medicine, a contrast agent or the like housed in the syringe into the blood vessel of a patient. By moving the plunger backward, it is possible to refill a liquid medicine, a contrast agent or the like into the syringe.
Such joint mechanism for a plunger and a piston has been disclosed by, for example, Japanese Patent Laying-Open No. 2004-290352 (PTD 1) and U.S. Pat. No. 4,677,980 (PTD 2).